Cathode-ray tube



June 12, 1951 H, S HADE 2,556,824

CATHODE-RAY TUBE Filed March 28, 1946 Sheets-Sheet 1 Ill I l p INVENTOR. 9H0 06919618 Patented June 12,1951

CATHODE-RAY' TUBE Otto-H. Schade West CaldwelLN; J assignor to; Radio: Corporation of America; a; corporation;

of Delaware.

Application March 28, 1946, SerialNo. csmo z This: invention relates to cathode ray beam pick-uptubes and more particularly to an ar rangement for obtaining" complete discharge of the target afterthe' signal has been utilized.

In cathode ray beam pick-up tubes in which the. beam. is. decelerated substantially to zero velocity at the target and" deposits electrons; in proportion tothe" charge-image, the discharge isnot always complete. Lowlight charges are therefore builtup exponentially during successive-"scansions to a higher value at which charge and-discharge areequal. This time lag reduces the sharpness of moving obj (acts. The residual charges; as Well as interline-charges remaining withlint'erlacedscanning, will causecolor carry over in color television, unless removed by a discharge process; I

In an attempt" to produce a complete dis= charge of thetarget aftereachline scansion, the beam: has heretofore beenshifted to a previously scanned I lineareas during lineretrace without shutting it off; but-With ail-increaseof intensity otab'out fifteen times 'thatof the normal 'strength during line trace; This has-been somewhat successful; but itisdificult to operate an electron gun'having-a small aperture, such as 2 mils; witlrsucha high density beam current and; further, this" procedure requires sp ecial deflecting means for the heavydischarge beam;

It isan object of thisinvention to'provide for theifull discharge-of a-cathode ray beam target without utilizing the normal beam aperture during line-retrace.

Anotherobject is to provide for the full discharge-"of the image through use of a separate beamcontrolled by the: normal 1 deflecting coils.

Other objects of theiinvention will 'appe ar in theefollowi-ng description, reference= being had to'the drawing; in which:

Fig. 1 is' an illustration .of a -cathode raytube embodyingithe invention.

Fig. 2.:is an end view of. the gun, illustrating the. relative. position of i the two b'eam' apertures in" relation to'the area scanned thereon by the return-beam;

Fig. 3 diagrammatically illustrates -a portion of the target; showing the discharge area of 'the heavy beam trailing the line-scansion of the normal'beam.

Fig. 4: contains a series of graphs illustrating the" principle: of i the invention;

Fig.1 5' is a circuit .diagram illustrating one way for: eliminating the undesiredpulse pro-'- duced by the clean-up. beam:

7 Claims. (Cl. 315-12) Fig. 6- shows amodification of thecontrol electrodes 7 1 Referring to the drawing, the evacuated envelope I of glass contains a target of transparentfmica having on'-one side a mosaic 2 Y capable of emitting photo-electrons'under the action of the light rays focused ther'eon from the object to: be televised; These: pass through a tran'se parent-metallic grounded coating 3 called-the signal-plate; At:the*opposite end' of the* tube is -locatecl the-gun of normalconstruction except that it projectss'two beams instead of oneth'rough theuseof two cath'odes 4, 5, two grids fi'; I--and an anode: 8: having. an. end S-With theusual small aperture II] and a larger aperture" H shown as dots in-Fig;- 2; Theanode end Q may act as the first dynode" oii a -multiplier, such as disclosed in the application of PauliK; Weimer, filed September-1631944, Seria1' No-.- 5544494; now U. SL Patent"2443.941; issued-Januarwfi; 1948. The. other. stages aoffthe multiplier are: indicated diagrammatically atAZ, .25, Stand;

The: envelope. I" alsocontainsthe usual elements-of flan orthicon tuoe; such :as-wall coating electrode" I3, decelerating ring': electrode= I 4 and a sci-called :ipersuader:ringelectrode IE ad'j'acent the-send :of: the gun: Outside the envelope-are locatedthe axially-I adjustable compensating-coil IS; the. usuaLvertical I and: horizontal deflecting coil unit' I? andithe=magneticfocusing. coilllB. Thefunctions of these: elements are similar to those described-in the said Weimer: application andneednot berfurther'referred to;

Thesb'e-am aperture I fl may be :of f'small idiameter, say. in' thewnei'ghborho0d lof 2: m-i1s; to pro duce La: beam I 9 of :"sufii'cient f intensity forvideo line-.scansicn; The: aperture I I maybe sufli ciently larger than" aperture: I66 to furnish :a beam 2B of 'suit'ab'l'ea intensityand" diameter to wipe out the: residual charges 5: in. chef. or more 'scansions across :the target during. line retrace time of the beam. I92 The direction of 'line'fi and frame scansionwistindicated byathe arrows .aga'nd b'inFig; 3.

The ;larger1 aperture 2 I I s is.-.placed afldistance -d, such". as 2 tent lines,. from: the: smaller: aperture lii-zsoazthat its wipe-offitracel l (Fig; 37 will trail a. suitable distance. behind. the lines not yet scanned .bytbeam I 9,: which distance should take itoutside thezareaZZ scanned on the first d-yno'de 91 by :thesignal ibeam' 2 3 i returning from the -target. This will. preventits: image frombeing passed:throughithezmultipliei" stages. The seconolaries tliberated under bombardment-bi the first dynode ile of the -multiplier:"are drawn'into the remaining stages 42, 25, 32 and 44, as explained in more detail later herein.

The grid 6 for beam 20 will be controlled by any known type of pulse generator, indicated by block diagram 24, so that it is keyed oil while the beam I9 is scanning a line and keyed on while that beam is on line retrace. It will be apparent that the heavy beam 20 will produce an undesired video signal during the retrace time of the small beam l9. This can be eliminated in various ways in the amplifiers to which the multiplier output is connected, but I have shown in Figures 1 and a preferred way of doing this. Figures 1 and 5 disclose a circuit means for providing a signal pulse to eliminate the undesired video signal produced by the retrace beam 20. The multiplier stages 42, 25, 32, and 44 are shown as connected, respectively, to points of different potential of an energy source, such as a battery 50. This provides an increasing positive potential on each successive stage. Collector 46, of the multiplier section 22, is the most positive of the multiplier parts and collects the amplified signal electrons after they have passed through the several stages. These signal electrons produce a pulse which provides a voltage change on grid 52 of an amplifier triode 36. The current through the triode amplifier is thus modulated by the grid 52 and may be further amplified to provide the video output signal of the system. At terminal 35 in the circuit joining collector 46 to amplifier grid 52, there is connected a triode 34, whose grid is connected to an adjustable grid circuit resister 34A, which in turn is connected to a pulse generator (not shown).

The video pulses produced by beam 20 during retrace are eliminated by reducing the voltage between any two of the multiplier stages, for example, the third and fourth, or 25 and 32 respectively. Graph I of Fig. 4 illustrates the output electron current, say of the third stage 25. The video signal of the beam I9 on line trace is shown at 26 and the undesired output of beam 20 is indicated at 21. Line 28 is zero current value and represents super white. Lines 29 and 30 represent normal white and black, respectively. During line retrace a negative voltage pulse is introduced at 3| by well-known generating means, such as a pulse generator indicated at 40. The voltage pulse is indicated by graph II at 21A and is of such value that it reduces the voltage on the fourth multiplier stage 32 to the voltage of the third stage 25, or below it. Thus, during line retrace no electrons are drawn into the fourth stage and this eliminates the undesired current produced during line retrace by beam 20, as indicated by graph III. However, the absence of electron current at 33 of this graph represents undesirable super white instead of the desired black. Therefore, I introduce into the multiplier output by means of tube 34 at point 35 (Figure 5) a pulse that is equaland opposite to the multiplied value of pulses 33, This is represented by graph IV, showing pulses 33A equal and opposite to pulses 33. The pulse in the adjustable grid circuit resistor 34a would, of course, be the reverse of graph IV. Thus, the video input to the amplifiers, represented for simplification by a single triode 36, would have the form shown by graph V, with the desired picture black value during line retrace.

It will be obvious that multiple grid tubes may be used in place of the triodes 34, 36. It will also be clear that the target of the tube in Fig. 1 may be of the two-sided type, as in the image orthicon, on which charges are produced by secondary electrons released by bombarding photo-electrons, as shown in said Weimer application.

The paths of beams I9 and 20 are controlled by the same deflection unit and the aperture of beam 20 may be made as large as required for complete discharge, so the prior art complications previously referred to are avoided.

The two beams may be produced in other ways than that disclosed. For example, one cathode would sufiice. The grids then would consist of two semi-circular discs, one with the small aperture and the other with the large aperture, as shown in Fig. 6. Also, two entirely separate guns may be used. The action in these cases would be exactly the same as that described.

Various other modifications may be used without departing from the spirit of the invention.

I claim:

1. An electron discharge device comprising, an electron gun structure for forming two electron beams along respective paths, a target electrode positioned transversely to said beam paths, means for scanning said electron beams over a surface of said target electrode, and a pulse generator circuit including said electron gun structure for keying one of said beams on only during retrace time of said other beam.

2. An electron discharge device comprising, an electron gun structure for forming two electron beams along respective paths, a target electrode positioned transversely to said beam paths, means for scanning said electron beams over a surface of said target electrode, said electron gun structure including a control grid surrounding the path of one of said electron beams, and a pulse generator circuit including said control grid for keying on said one electrode beam only during retrace time of said other beam.

3. A television signal transmitting device comprising an envelope, an electron gun structure for forming two electron beams along two respective paths within said envelope, a target electrode positioned within said envelope transversely to said beam paths and including an insulator sheet adapted to have a charge distribution formed thereon, means for producing line scansion of said electron beams over a surface of said insulator sheet, a collector electrode within said envelope for receiving electrons from said insulator surface, said electron gun structure including a control electrode surrounding the path of one of said electron beams, and a pulse generator circuit including said control electrode for keying on said one electron beam only during retrace time of said other beam.

4. A television signal transmitting device comprising an envelope, an electron gun structure for forming two electron beams along two respective paths within said envelope, a target electrode positioned within said envelope transversely to said beam paths and including an insulator sheet adapted to have a charge distribution formed thereon, means for producing line scansion of said electron beams over a surface of said insulator sheet, an electron multiplying means including a plurality of dynode electrodes for receiving reflected beam electrons from said insulator target surface, said electron gun structure including a control electrode surrounding the path of one of said electron beams, and a pulse generator circuit including said control electrode for keying on said one electron beam only during retrace time of said other beam, and a circuit means including two of said dynode electrodes and a second pulse generator for maintaining said two dynode electrodes at the same potential only during said retrace time of said other beam.

5. A television signal transmitting device comprising an envelope, an electron gun including an electron source and electrode structure for forming two electron beams along respective paths within said envelope, a target electrode positioned within said envelope transversely to said beam paths and including an insulator sheet, a conductive layer on one face of said sheet and a photosensitive layer on the other face of said sheet, circuit means connected to said conductive target layer for maintaining said conductive layer and said electron source at a common potential during operation, means for producing line scansion of said electron beams over a surface of said photosensitive layer, an electron multiplying means including a plurality of dynode electrodes for receiving reflected beam electrons from said photosensitive target layer, said electron gun structure including a control electrode surrounding the path of one of said electron beams, and a pulse generator circuit including said control electrode for keying on said one electron beam only during retrace time of said other beam, and a circuit means including two of said dynode electrodes and a second pulse generator for maintaining said two dynode electrodes at the same potential only during said retrace time of said other beam.

6. The method of operating an electron tube having a photosensitive film coating one face of an insulator sheet, said method comprising the steps of producing a charge distribution on said photosensitive film, line scanning an electron beam over the surface of said photosensitive film to discharge said charge distribution, scanning said photosensitive film with a second beam only during retrace time of said first beam to completely discharge said photosensitive film.

7. The method of operating an electron tube having a photosensitive film coating one face of an insulator sheet, said method comprising the steps of producing a charge distribution on said photosensitive film, line scanning an electron beam over the surface of said photosensitive film to discharge said charge distribution, scanning said photosensitive film with a second beam only during retrace time of said first beam to completely discharge said photosensitive film, reducing said electron beams to substantially zero velocity adjacent said target surface whereby the electrons of said beams not discharging said target are reflected, collecting the reflected electrons of said beams by a multiplier section having a plurality of dynode electrodes, maintaining an adjacent pair of said dynode electrodes at a common potential only during retrace time of said first beam.

OTTO H. SCHADE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,227,484 Bouwers Jan. 7, 1941 2,260,911 Knick et a1 Oct. 28, 1941 2,276,359 Von Ardenne Mar. 17, 1942 2,335,983 Wilson Dec. 7, 1943 2,345,282 Morton Mar. 28, 1944 

